1. Field of the Invention
The present invention relates to filtration devices, novel methods for the production of the same and methods of use. More specifically, the present invention relates to a methodology of vibrating and then sintering polymers having distinct morphologies to achieve a structural filtration matrix, which is also capable of accommodating various compounds for the removal, reduction or adsorption of undesirable contaminants in liquids and gases, most notably water and air.
2. Description of the State of Art
The filtration of fluids may be accomplished through a variety of technologies, the selection of which is often determined by the contaminant or contaminants that are being targeted for removal or reduction. Particulates are best removed through a process known as depth filtration. The filter collects and holds any dirt or sediment within its matrix. Dissolved organic contaminants appearing on a molecular level may be removed through adsorption or, in the case of minerals and metals, through ion exchange. Very small contaminants, including microorganisms down to sub-micron sizes often require some form of membrane technology in which the pores in the membrane are configured to be smaller than the target contaminant; or they can be deactivated in some manner. Contaminants in drinking water may be broken down into four groups: (i) turbidity and particulates; (ii) organic based chemicals and pesticides; (iii) inorganic matter such as dissolved heavy metals that pose a health risk such as lead; and minerals; (iv) microorganisms such as protozoan parasites, bacteria and viruses. While there is a specific technology for the treatment of each group, some filters are designed to treat several contaminant groups through a single filtering technology. Since organic contaminants have historically been the most common, activated carbon has been used to remove a wide spectrum of contaminants from liquids, most notably drinking water. For this and other reasons most prior art fluid filters are carbon based and commonly known as carbon blocks. The current invention relates to an alternative approach to removing contaminants from fluids that provides superior filtration of fluids and other improvements over prior art methodologies.
Plastics have long been used for filtering fluids. Such methods generally involve taking plastic pellets and cryogenically grinding them into a granulated and/or powdered form. This resulting material could be used as produced or it could be screened through a sieve to separate the particles into more tightly controlled mesh ranges. The plastic particles are then sintered in a mold. The process, known more specifically as porous plastics, involves taking the mold filled with the plastic material up to a temperature where the particles soften but do not melt, such that all of the particles stick to one another. The mold is then brought back to ambient temperature and the material is ejected from the mold. The finished part is at the same time solid and self-supporting while being porous to fluids. Any plastic that can be ground into a granular form can be used; and some polyethylene polymers are produced in a powder form. Finer particles create a matrix of smaller spaces between the plastic particles which are known as voids or pores. Filtering materials, including but not limited to activated carbon, may be added to enhance the filtration of a specific contaminant. The process of blending into and holding within the matrix of the polymeric material other filtering compounds requires that the total surface area of the polymer be greater than the total surface area that the added materials take up, such that there is sufficient adhesion. When formulated accordingly, the resulting part is durable and self-supporting. Where both the polymeric material and the filtration compounds selected generally share a similar bulk density and particle size the preferred ratio by weight for most filtration applications provides that at least 50% to 60% of the filter by weight be polymeric particles. In this process there is no force, compression nor pressure applied to the materials before or during processing, such that both the polymer particles and the filtering materials remain essentially in tact (i.e. they do not lose their original shape). The fluid being filtered flows through the porous matrix where it is forced into contact with the adsorbents or other filtering materials. This filtering technique, known as tortuous path filtration differs from what is known as absolute filtration. The size of the median diameter of the pores within the porous plastic filter determine how much of any given contaminant by size will be allowed to pass through the filter matrix. These pores cannot be made to a consistent single size and generally range from large to small, with the filter being measured by its median pore diameter (MPD) as determined by a mercury poresimiter analysis. The median pore diameter may be manipulated, as stated above, to be larger or smaller by manipulating the size of the particles that comprise it. This includes both the particle sizes of the plastic granules or powders as well as any material being blended into it.
An alternative method of filter making is known as carbon block technology. Carbon blocks are molded granular activated carbon particles. The origin came from the need to improve upon the use of loose bed carbon particles that have been utilized to remove organic contaminants from water since Roman times. However, loose bed activated carbon filters lack performance in specific areas and, as a practical matter, take up too much space for many point-of-use applications. These drawbacks led to the development of the carbon block technology during the 1980s. Here, carbon particles are blended with a small amount of a thermoplastic material, known as the binder, in a general ratio of about 4 parts granular activated carbon to 1 part thermoplastic material. The material is thoroughly blended together, poured into a cylinder shaped mold and compressed so as to compact the blended material as much as possible. The material is then heated to a point where the binder either softens or melts to cause all of the carbon particles to adhere to one another. The adhesion process uses only a small amount of binder in a ratio to activated carbon granules, which is aided by the compression that is applied to the two materials during processing. Once cooled the finished part takes on the form of a solid cylinder block comprised of carbon particles, which is self-supporting while being porous to most fluids. The cylinders invariably are tube shaped such that there is a core and a wall thickness. Water is directed to flow radially from the outside diameter (OD) surface of the tube to the inside diameter (ID) and then out one end of the core.
The ability to bond carbon particles together in a fixed bed enables carbon filters to use finer carbon particles than those traditionally used in loose bed filtering methods. The use of finer particles in turn increased the amount of available surface area of the adsorbent activated carbon, while compression of the particles during processing increased the density of carbon particles. This density also contributes to increasing the absolute micron rating of the filter since voids between the carbon particles are eliminated, creating an absolute barrier to the passage of particulates. The Degen and Vanderbilt patents (U.S. Pat. Nos. 4,664,683 and 4,753,728, respectively), both filed in 1986, teach the use of binders used in carbon block technology. Vanderbilt disclosed the use of high density polyethylene polymers in lieu of other binders, including the use of an ultra high molecular weight polyethylene (UHMW) polymer specified as GUR 212. In 1991 Koslow, in his U.S. Pat. No. 5,019,311, disclosed an alternative method of carbon block manufacture in which the adsorbent activated carbon may be blended with a combination of very low melt temperature binders and driven through an extrusion tube by an auger. The blended material is compressed as it is conveyed into the extrusion tube, then heated and quickly cooled to produce an extruded carbon block.
In the filtration of fluids, especially water and air, carbon block methodologies have certain limitations which the current invention overcomes. Carbon blocks are limited to the use of only one primary filtering material: activated carbon granules, without which there is no filter. Further limitations include the lack of depth filtration and durability. Carbon block filters exhibit a high pressure drop as a result of the compression used during processing. Fluid filters made using the current invention's methodology combined with specific polymers represent a major departure from prior art filter making methods. The current fluid filter invention may incorporate any filtering material without reliance on any single material, including very fine powders smaller than one micron. Resulting filters differentiate from prior art methods in that they exhibit superior filtration performance, excellent depth filtration, a very low pressure drop, durability, and they may be molded into any shape or dimension.
There is still a need, therefore, for a filtration device wherein the structural matrix of the filter is independent from the filtration compounds, and where the smallest particle size of the filtration compounds is unlimited, such that advantage may be taken of the greater surface area of finer powders. This in turn will allow the filtration device to be formulated to meet a specific task or tasks, while at the same time exhibiting a number of superior performance features and benefits over other filter assemblies. There is a further need for a filtration device that is durable, displays enhanced depth filtration, and exhibits minimal pressure drop.